Clamps are commonly used for securing workpieces to machine tables during machining operations such as drilling and milling. Edge clamps and toe clamps are frequently used. Machine operations can apply large vertical, lateral, and torquing forces on the workpiece or part being machined. The large tool forces require large counteracting clamping forces to prevent the part being machined from moving out of tolerance or flying off the machine table entirely. The clamping force requirement is exaggerated in the case of small parts being machined. In the first place, the small part typically has only a small surface area upon which a clamping force can be brought to bear. In the second place, the size of the clamping device may be of large size relative to the part being machined and can obscure tool access to a significant portion of the part, especially the part sides.
In one device, the ADVANT-EDGE.TM. edge clamp, a body having an inclined surface is provided along with means for securing the body to a T-slot. A nominally rectangular clamping element, having a small bore hole therethrough and a larger round surface recess, is disposed on the incline and held in place upon the incline with a bolt extending through the recess and bore hole. The bolt has a round head mounted on the end of the bolt shaft and off center from the shaft. This mounting provides a small distance from shaft center to head outside edge on one side, and a large distance from shaft center to head outside edge on the opposite side. As the head is rotated, the bolt is drawn in at an angle perpendicular to the incline, and the wider portion of the head rotates as a cam down the incline, and toward the workpiece being held. The clamping element is forced slightly downward and toward the workpiece. There are several drawbacks with this design. First, to allow the bolt to rotate, the clamping element must be spaced above the incline surface with a gap therebetween to allow the bolt to turn, otherwise the bolt would be bound. This results in tilting or deflection of the clamping element from vertical as it is advanced into contact with a workpiece, which translates into a less than firm grip on the workpiece. Second, the bolt increases force on the workpiece only through 180.degree.. Further turning of the bolt decreases the applied force over the next 180.degree. and the clamping element cannot be drawn tight to the incline surface.
In U.S. Pat. No. 4,049,253 to Mandel, a toe clamp is described including a work-engaging member, a nut, an inclined clamping screw for tightening the work-engaging member to the bolt, and an inclined shoulder bolt having a non-threaded region disposed within the work-engaging member and a threaded region disposed within the nut. The toe clamp described has the work-engaging member apart from, and not received by, the nut. Only the shoulder bolt threaded lower region is received by, and receives any support from, the nut. Finally, the work-engaging member is disposed totally above the table top. The toe clamp work-engaging member described is believed to be prone to some tilting or deflection about the screw and shoulder bolts. The work-engaging member resides totally above the work table surface, blocking machine tool access to a substantial part of the workpiece, as can be seen from inspection of FIG. 4 of the reference.
What would be desirable is a workpiece clamp having improved support for the workpiece engaging member, which eliminated or reduced any deflection of the clamping element from vertical while contacting the workpiece to provide consistent workpiece placement. What would further be desirable is a workpiece clamp having most of the structure disposed below the work table surface, enabling machine tool access to a substantial portion of any parts being machined, while achieving improved support for the workpiece. What would also be desirable is a workpiece clamp having improved workpiece-holding characteristics.